1. Field of the Invention
This invention relates to a method of obtaining composite ion exchangers which are formed as a result of implanting inorganic sorbents or ion exchangers of specific sorptive properties into a polycondensation matrix of an organic carrier.
2. Description of the Prior Art
Numerous inorganic sorbents and ion exchangers are strongly selective in relation to some metal ions. For example, ferrocyanides of bivalent metals efficiently sorb cesium ions, while hydrated oxide of pentavalent antimony selectively sorbs sodium ions from acidic solutions. Ferrocyanide sorbents are widely applicable for purifying liquid radioactive wastes from .sup.137 Cs (V. Pedarek, V. Vesely, Talanta, 19, 1972, 1245). Hydrated antimony pentoxide is frequently used in neutron activation analysis to remove .sup.24 Na from activated samples of biological materials (A.K.De, A.K.Sen, Sep.Sci.Techn., 13, 1978, 517).
However, the inorganic sorbents have some disadvantageous properties, undesirable in practice, such as poor mechanical strength, irregular shape of the sorbent grains, relatively high solubility in water, slow kinetics of the ion exchange process, as well as rather high density (C.B.Amphlett, "Inorganic Ion Exchangers", Elsevier Publ.Co., Amsterdam, 1964).
Several methods are known to modify some properties of the inorganic sorbents, wherein the sorbents are transformed into composite materials. For instance, some inorganic sorbents are deposited on carriers such as anion-exchange resins (K.Watari, K.Imai, M.Izawa, J.Nucl.Sci.Technol., 4, 1967, 190) or inorganic sorbents (R.Caletka, C.Konecny, Radiochem. Radioanal. Letters, 12, 1972, 325). Other composite sorbents are obtained by processing powdered inorganic sorbents with various polymers dissolved in organic solvents, followed by evaporation of the solvent (J.Stejskal et al, J. Radioanal. Chem., 21, 1974, 371). It is in this way that composite ferrocyanide sorbents (S.U. Pat. No. 1,012,969, Apr. 23, 1983) as well as composite aluminosilicate sorbents (U.S. Pat. No. 4,316,819, Feb. 23, 1982) were obtained in order to improve stability and to decrease solubility in water of the inorganic filler. However, the above mentioned methods are not always efficient in producing the composite sorbents of required physico-chemical properties.
Another method allows to obtain the composite sorbents in the form of spherical beads by adding some metal salts or oxides to the reaction mixture in the polycondensation process of phenols and aldehydes, followed by processing the obtained product with aqueous solutions of alkalia, which transforms the implanted salts or oxides into active inorganic sorbents (Jap. Pat. No. 5,969,151, Apr. 19, 1984). There is still another way to obtain composite sorbents of hydrated titanium, zirconium, or stannic oxide in organic matrices, based on curing a mixture consisting of one of the given metal oxides and an epoxy, unsaturated polyester or polyurethane resin (U.S. Pat. No. 4,362,626, Dec.7, 1982). Large but still limited number of the composite sorbents can be obtained using the above methods.